Catalytic oxidation of carbon monoxide and dimethyl ether synthesis over gold-containing catalysts

摘要

In recent years, the catalytic properties of finely dispersed gold particles on oxide supportudmaterials have attracted much attention. Such catalysts are active for several types ofudoxidation reactions, in particular low-temperature carbon monoxide oxidation. The watergas-udshift (WGS) reaction and the selective oxidation of CO in the presence of hydrogenudare possible applications of gold-based catalysts.udIn this thesis we attempted to detail the key issues relevant to the deactivation ofudsupported gold catalysts. A new aspect of the CO oxidation deactivation mechanism wasudcomprehensively discussed. It was found that titanate nanotube supported gold catalystud(Au/TN), prepared by deposition precipitation, deactivated due to the formation ofudbicarbonate species on gold-sites. Moisture prevented the formation and accumulation ofudthese species and also promoted the reaction. The Au/TN catalyst was characterised byudHRTEM, in-situ DRIFTS-Mass spectrometry, BET, etc.udTitanium dioxide (TiO2) is widely used as support material for various importantudindustrial catalysts and its modification may suite specific catalytic requirements. In thisudwork we have confirmed that the incorporation of nitrogen (N) into TiO2 increases theudconcentration of oxygen ion vacancies. When tested for CO oxidation, the nitrogendopedudtitania supported gold catalyst, Au/TiO2-xNx, was found to be a poor and unstableudcatalyst compared to the pure titania supported gold catalyst, Au/TiO2. Both catalystsudwere characterised by XRD, Raman spectroscopy, DRS-UV visible spectroscopy, TPO,udBET, HRTEM etc.udNew Cu-based methanol synthesis catalysts, prepared by co-precipitation and depositionudprecipitation, were physically mixed with _-Al2O3 and tested for the direct single-stepudDME synthesis from syngas. The catalysts exhibited good CO conversion and DMEudselectivity. The loading of gold on the methanol synthesis components of the bifunctionaludcatalysts promoted CO conversion and the WGS reaction. In addition, Au suppressedudivudmethanation on the bifunctional catalysts. The catalysts were characterised by TPR,udXRD, BET and XRF spectroscopy.